Certain complexing agents may be used to remove carbon monoxide, ethylene, and/or acetylene from gas mixtures by methods disclosed, for example, in U.S. Pat. Nos. 3,592,865; 3,651,159; 3,754,047; 3,755,487; 3,758,606; 3,758,607; 3,845,188; and 3,857,869.
The methods disclosed in these patents generally employ sorbents of the formula CuAlX.sub.4, where X is a chlorine, fluorine or bromine atom, in a C.sub.6 -C.sub.20 aromatic solvent. The sorbent is able to form complexes with CO, ethylene, and acetylene, which complexes may be treated to release the gases complexed separately from the remainder of the original gas mixture, and the sorbent regenerated.
It has been observed that in a gas mixture of the type described above the cuprous aluminum halide sorbent will absorb the ethylene in preference to the carbon monoxide. However, the stream should be free of water, methanol, CS.sub.2, and H.sub.2 S since they react with the sorbent; propylene and heavier unsaturated hydrocarbons are complexible and may interfere with a desired process of ethylene, carbon monoxide, or acetylene removal. Accordingly, such compounds as water, methanol, CS.sub.2, H.sub.2 S, and unsaturated hydrocarbons above ethylene should be removed before passing the mixture to the complexing solution where ethylene, carbon monoxide, or acetylene is to be recovered preferentially.
Prior to the present invention, it was known to use the liquid sorbent itself (U.S. Pat. Nos. 3,960,910 and 3,927,176) to remove the impurities. It has also been common, of course, to remove various impurities from gases by other means.
Processes which might remove water, methanol, carbon disulfide, hydrogen sulfide, propylene, and heavier unsaturated hydrocarbons from a gas containing ethylene, acetylene, and/or carbon monoxide can be grouped into two categories -- fixed-bed adsorption systems and solvent-absorption systems.
A typical fixed-bed adsorption system contains two adsorbent beds in parallel. At any given time, one bed is on-stream and the other undergoing regeneration. At regular intervals (before the on-stream unit becomes saturated with contaminants), the roles of the beds are reversed. Steam or hot gas is used for regeneration. Disadvantages associated with the use of adsorption processes for the above separation are (1) complex and expensive control systems would be required for their operation; (2) an excessive amount of energy would be consumed for regeneration of the beds; (3) at the temperatures encountered in regeneration, polymerization of unsaturates adsorbed on the beds would occur; and (4) a substantial amount of ethylene and acetylene would be co-adsorbed with the contaminants and would subsequently be lost during regeneration.
Solvent-absorption systems typically contain two columns -- an absorber and a stripper. The unit is operated continuously and control is relatively simple. Lean solvent entering the top of the absorber descends countercurrently to the gas flow and absorbs the contaminants from the gas. The solution is heated and enters the stripping column, where the solvent is regenerated by boiling off the absorbed contaminants. A considerable amount of the product gas may be co-absorbed with the contaminants, but its loss can be avoided by flashing or prestripping the rich solvent and recycling the vapor formed to the absorber feed. However, for the separation described above, polymerization of unsaturated compounds could occur in the stripper and would rapidly foul its reboiler and trays.
Various other methods of removing certain components for gas mixtures are also known. However, it is believed that no one has assembled the series of units and steps which we employ; no one has prepared a gas derived from coke oven gas for ethylene removal by cuprous aluminum halide absorbent solutions.